RESUMO
Immediate early gene expression in the CNS is induced by sensory stimulation and seems to be involved in long-term synaptic plasticity. We have used an immunohistochemical method to detect the nerve growth factor-induced gene A (NGFI-A) protein expression in the superficial layers of the rat superior colliculus during postnatal development. Our goal was to correlate the expression of this candidate plasticity protein with developmental events, especially the activity-dependent refinement of the retinocollicular and corticocollicular pathways. We have also investigated the N-methyl-D-aspartate (NMDA)-receptor dependence of the NGFI-A expression. Animals of various postnatal ages were used. Postnatal day (P) 12 and older animals were submitted to a protocol of dark adaptation followed by light stimulation. NGFI-A expression was never observed during the first 2 postnatal weeks. The first stained cells were observed at P15, 2 days after eye opening (P13). The highest number of stained cells was observed at the end of the third postnatal week (P22). Adult-like level of expression was reached at P30, since at this age, the number of stained cells was comparable to that found in adult rats (P90). Both P22 animals submitted to an acute treatment with MK-801 (i.p. injection) and adult animals submitted to chronic intracranial infusion of a MK-801 presented a clear decrease in the NGFI-A expression in response to light stimulation. These results suggest that the NGFI-A expression is dependent on the NMDA receptor activation, and the observed pattern of expression is in close agreement with previous descriptions of the changes in the NMDA receptor-mediated visual activity in the developing rat superior colliculus (SC). Our results suggest that the plasticity-related NGFI-A protein might play a role in the developmental plasticity of the superficial layers of the rat SC after eye opening.
Assuntos
Proteínas de Ligação a DNA/biossíntese , Proteínas Imediatamente Precoces/biossíntese , Plasticidade Neuronal/fisiologia , Receptores de N-Metil-D-Aspartato/metabolismo , Colículos Superiores/crescimento & desenvolvimento , Colículos Superiores/metabolismo , Fatores de Transcrição/biossíntese , Vias Aferentes/efeitos dos fármacos , Vias Aferentes/crescimento & desenvolvimento , Vias Aferentes/metabolismo , Animais , Animais Recém-Nascidos , Proteínas de Ligação a DNA/genética , Adaptação à Escuridão/fisiologia , Maleato de Dizocilpina/farmacologia , Proteína 1 de Resposta de Crescimento Precoce , Antagonistas de Aminoácidos Excitatórios/farmacologia , Proteínas Imediatamente Precoces/genética , Imuno-Histoquímica , Estimulação Luminosa , Ratos , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Fatores de Transcrição/genéticaRESUMO
The postnatal development of mediodorsal thalamic projections to the dorsomedial frontal cortex of mice was assessed by means of the retrograde peroxidase-colloidal gold complex tract tracing system. The tracer was injected into the dorsomedial frontal cortex from the day of birth (P0) to 60 days of postnatal age (P60). Since birth, a dense retrograde labeling has been found in the mediodorsal nucleus, which increased progressively from P4 to P8 and began to decrease at P10 until P13 (67.37% vs. the maximal average, P4). After P16, the mean average remains stable up to P60.
Assuntos
Vias Aferentes/crescimento & desenvolvimento , Diferenciação Celular/fisiologia , Núcleo Mediodorsal do Tálamo/crescimento & desenvolvimento , Neurônios/citologia , Córtex Pré-Frontal/crescimento & desenvolvimento , Vias Aferentes/citologia , Envelhecimento/fisiologia , Animais , Animais Recém-Nascidos , Coloide de Ouro , Núcleo Mediodorsal do Tálamo/citologia , Camundongos , Córtex Pré-Frontal/citologia , Conjugado Aglutinina do Germe de Trigo-Peroxidase do Rábano SilvestreRESUMO
Serotonin (5HT) is expressed transiently in primary sensory areas of the rat neocortex during the establishment of the thalamo-cortical topography and somatotopy. The precise role of 5HT during the specification of neocortical areas is still uncertain. We evaluated the effects of increasing and decreasing cortical serotonin concentrations on the specification of the barrel cortex using a rat model of isocaloric undernutrition. This manipulation increases brain 5HT levels during brain development. Undernourished animals were also treated with p-clorophenylalanine; an inhibitor of 5HT synthesis. Barrels representing the head were readily seen at postnatal day 5 in control and p-clorophenylalanine treated rats. In contrast, undernourished rats treated or not with p-clorophenylalanine showed no barrels representing the head but until postnatal day 7. Chromatographic analyses demonstrated that the concentration of cortical 5HT increased by 50% in undernourished pups during barrel field formation. Control and undernourished animals treated with p-clorophenylalanine had a significant reduction (90%) of 5HT in the cortex. The overall geometry of the barrel field and of individual barrels was similar among animal groups. Our results support that 5HT plays a small role in triggering and timing barrel field somatotopy.
Assuntos
Vias Aferentes/crescimento & desenvolvimento , Vias Aferentes/metabolismo , Padronização Corporal/fisiologia , Diferenciação Celular/fisiologia , Privação de Alimentos/fisiologia , Serotonina/deficiência , Córtex Somatossensorial/crescimento & desenvolvimento , Córtex Somatossensorial/metabolismo , Vias Aferentes/efeitos dos fármacos , Animais , Animais Recém-Nascidos , Padronização Corporal/efeitos dos fármacos , Peso Corporal/efeitos dos fármacos , Peso Corporal/fisiologia , Diferenciação Celular/efeitos dos fármacos , Fenclonina/farmacologia , Núcleos da Rafe/efeitos dos fármacos , Núcleos da Rafe/crescimento & desenvolvimento , Núcleos da Rafe/metabolismo , Ratos , Ratos Wistar , Antagonistas da Serotonina/farmacologia , Córtex Somatossensorial/efeitos dos fármacos , Vibrissas/inervação , Vibrissas/fisiologiaRESUMO
Since 1890 Ramón y Cajal strongly defended the theory that dendrites and their processes and spines had a function of not just nutrient transport to the cell body, but they had an important conductive role in neural impulse transmission. He extensively discussed and supported this theory in the Volume 1 of his extraordinary book Textura del Sistema Nervioso del Hombre y de los Vertebrados. Also, Don Santiago significantly contributed to a detailed description of the various neural components of the hippocampus and cerebral cortex during development. Extensive investigation has been done in the last Century related to the functional role of these complex brain regions, and their association with learning, memory and some limbic functions. Likewise, the organization and expression of neuropsychological qualities such as memory, exploratory behavior and spatial orientation, among others, depend on the integrity and adequate functional activity of the cerebral cortex and hippocampus. It is known that brain serotonin synthesis and release depend directly and proportionally on the availability of its precursor, tryptophan (TRY). By using a chronic TRY restriction model in rats, we studied their place learning ability in correlation with the dendritic spine density of pyramidal neurons in field CA1 of the hippocampus during postnatal development. We have also reported alterations in the maturation pattern of the ability for spontaneous alternation and task performance evaluating short-term memory, as well as adverse effects on the density of dendritic spines of hippocampal CA1 field pyramidal neurons and on the dendritic arborization and the number of dendritic spines of pyramidal neurons from the third layer of the prefrontal cortex using the same model of TRY restriction. The findings obtained in these studies employing a modified Golgi method, can be interpreted as a trans-synaptic plastic response due to understimulation of serotoninergic receptors located in the hippocampal Ammon's horn and, particularly, on the CA1 field pyramidal neurons, as well as on afferences to the hippocampus which needs to be further investigated.